1. Field of the Invention
The present invention relates generally to the field of sorting of recycled materials, and more particularly, but not by way of limitation, to methods and apparatus for optimizing the operation of an adjustable sorting apparatus or sorting system.
2. Description of Prior Art
Materials Recovery Facilities (MRFs) have been receiving and processing recyclable materials for the past 25 years. The recyclable material normally consists of newspaper, plastic bottles, steel and aluminum cans, and sometimes glass bottles and fragments. The newspaper stream was typically kept separate from the containers. During the first five to ten years the processing typically involved conveying the recyclables under a magnet to remove the steel, then past an air stream to separate the plastic and aluminum cans from the glass bottles. The rest of the components were then sorting manually by hand.
In the mid 1980s eddy current separators were introduced to automatically remove the aluminum from the plastic bottle and aluminum can stream. Then in the mid 1990s separation modules became available to separate the plastic bottles by resin type and by color. These separators did not, however, begin use in MRFs until around 1998. At about the same time the first system to automatically sort office paper was introduced by the assignee of the present invention (MSS, Inc.) in collaboration with Weyerhaeuser Company. An example of those systems is seen in U.S. Pat. No. 6,250,472 to Grubbs et al., assigned to assignee of the present invention and the details of which are incorporated herein by reference.
Mechanical screens saw limited use in MRFs until the late 1990s when the first cardboard screens were introduced. These screens were used to remove oversize cardboard from the newspaper stream. With the introduction of so called “single stream” collection in the late 1990s, however, screen technology was improved to address sorting of containers (i.e. plastic and glass bottles and metal cans) from the mixed paper and cardboard stream.
The first generation of screens involved either one or two flat bed screen “decks” which were inclined in the direction of motion of the material. The screens themselves were comprised of a number of discs attached to rotating shafts. In operation, the more 3 dimensional materials such as containers would tend to roll or bounce down the screen deck while more 2 dimensional materials such as newspaper and cardboard would go up and over the top of the screen. An example of inclined flat bed rotary disc screens is seen in U.S. Pat. No. 6,250,472 to Grubbs et al.
This screen technology evolved to where the angle of the screen, as well as the rotor speed, was adjustable to compensate for differing material composition and moisture content. The latest generation screen patented by CP Manufacturing is in the shape of a wide bottom V, with the entire V bottom tilted from horizontal. This screen has additional adjustable settings with include not only the rotor speed and tilt angle of the V sides, but also the tilt angle of the entire V. In this screen the paper is propelled by the discs up and over each side of the V. The containers roll back from the sides of the V and migrate down the bottom of the V in the direction of the tilt. Examples of such V shape rotary disc separators are seen in U.S. Pat. No. 6,460,706 to Davis and U.S. Pat. No. 6,648,145 to Davis et al., the details of which are incorporated herein by reference.
Unfortunately, however, very few MRF operators are capable of determining the optimum operating parameters for these new screens. Experience in MRFs also shows that even when the screens are properly set for a certain mixture of recyclables and moisture content, that setting is only good for a matter of a few minutes as the composition and moisture content changes.
FIG. 1 schematically illustrates the flow of material through a typical prior art Materials Recovery Facility (MRF) generally designated by the numeral 10. An input waste material stream 12 enters the MRF 10. As indicated at block 14 oversized and non-recyclable objects are removed by hand.
As indicated at block 16 a screening device may be used to separate large cardboard items which go to a cardboard destination 18. The bulk of the material which is made up typically of containers of various types and newspaper goes to a mechanical screening device 20 which separates the newspaper from the containers. The mechanical screening device 20 may for example be an adjustable angle trough-shaped screen such as those shown for example in U.S. Pat. Nos. 6,648,145 and 6,460,706.
The screening device 20 separates the material stream into a first stream or paper stream 22 which includes some containers, and a second stream or container stream 24 which includes some paper.
Typically the paper stream 22 is hand sorted as indicated at block 25 into a container destination 26, a paper destination 28, a contaminant destination 30, and with ferrous and aluminum materials directed to destinations 34 and 44, respectively.
The container stream 24 from separator 20 then passes through a magnetic separator 32 which removes ferrous items into a ferrous metal stream 34. The container stream continues at 36 to a hand sorting location 38 where newspaper is removed at 40 and returned to the newspaper destination 28, and the containers are hand sorted into plastic containers which go to destination 42 and aluminum containers which go to destination 44.
The plastic containers at destination 42 are then again hand sorted as indicated by block 46 into PET (Polyethylene Terephalate) containers to destination 48, colored HDPE (High Density Polyethylene) to destination 50, and natural HDPE (High Density Polyethylene) to destination 52.
What is needed then is a way to optimize the screen parameter settings and to modify those settings in real time as the composition and moisture content of the feedstream changes continuously. Even when set optimally the screens are not 100% effective. Containers (particularly flat ones) are sometimes carried over with the paper fraction, and as well some paper is carried along with the containers.
What is also needed is a way to optimize all of or a portion of a Materials Recovery Facility which includes one or more adjustable screens.